Toby Beveridge

Positron emission imaging using acquired cone-surfaces from opposing compton cameras

The Compton camera, a method of electronic collimation, introduces angular resolution into a gamma-ray imaging system without the need of a collimating device. Compton kinematics are used to deduce the incident trajectory of the photon, resulting in a cone-surface of possible source locations. So far this type of system has been successfully employed only as a single photon detection device. However, it has been proposed that positron emission tomography may also be enhanced by implementing the Compton camera. Cone-surfaces acquired from the collinear gamma rays produced in positron annihilation may be used to validate the resulting line of response. Moreover, single sided detections need no longer be redundant in image reconstruction due to the ability to perform cone-surface reconstruction in tandem with reconstruction from LoRs

Compton imaging using the SmartPET detectors

Image reconstruction from Compton camera data is a complex problem requiring investigation. Generally reconstruction is conducted using iterative reconstruction methods such as Maximum Likelihood - Expectation Maximization (MLEM). However, iterative reconstruction into volumetric grids is a computational burden. Analytic methods of image reconstruction have been proposed which relieve the computational expense. However, such methods usually have unrealistic sampling assumptions or are not directly extendable to situations where the scattering detector is extended when compared to the detector-source distance. Starting from a standard inversion technique, a generic method of filtering inversion co-efficients is developed. By dynamically assigning the strength of co-efficients on an event-by-event basis, artifacts arising from the difference between assumed and actual forward transform may be reduced. Dynamic assignment allows inversion of single cone-surfaces, so that the generic technique may be implemented in volumetric reconstruction. Results are compared to direct-back-projection in a limited-angle tomography context. The ability to apply event-by-event analytic image reconstruction provides many advantages when compared to standard iterative techniques.

Orthogonal Strip HPGe Planar SmartPET Detectors in Compton Configuration

The evolution of germanium detectors over the last decade has lead to the possibility that they can be used in medical imaging and security scanning. The potential of increased sensitivity and energy resolution that germanium affords takes away the necessity of mechanical collimators that would be required in a gamma camera. Without mechanical collimation the resulting increase in statistics leads to the possibility of decreased patient dose or increased system throughput. In terms of security imaging segmented germanium provides directionality and excellent spectroscopic information for nuclide identification.

High-purity germanium strip detectors -possible applications to SR studies

Developments in position-sensitive spectroscopic detector systems resulting from work undertaken in the fields of astrophysics, high energy physics and medical imaging provide an opportunity for the synchrotron physics community to look at possible improvements to synchrotron studies. Specifications of the detector designed by the smartPET collaboration are outlined; a brief comparison with current options presented and possible applications to X-ray imaging, protein and macromolecular crystallography and X-ray fluorescence holography are introduced.